1. Field of the Invention
The present invention relates to a light source device and a device for reading an original and method for producing light for reading an original. In particular, the present invention relates to a light source device that emits light which is irradiated onto an illuminated body such as an original, a device for reading an original by converting the light that has passed through the original or the light that has been reflected by the original into electrical signals, and a reading method for an original that can be used by the device.
2. Description of the Related Art
Conventionally, a device for reading an original is known having a structure for reading an image (i.e. image data representing density values for each pixel of the image recorded on the original is obtained) in which light emitted from a light source and passed through an original such as a photographic film on which an image has been recorded is photoelectrically converted for each pixel by a reading sensor such as a CCD and signals obtained from the photoelectric conversion are converted into digital data. Halogen lamps have been widely used as the light source in this type of device for reading an original, however, recent years have seen progress in the light intensification of LEDs. As LEDs have the advantages of being less expensive, smaller, and consuming less power than halogen lamps, LEDs have also become common as light sources in devices for reading an original.
It should be noted that a device for reading an original is capable of reading various types of film such as negative film and reversal film, for example; however, as is shown in FIG. 13, the spectral transmission density characteristics (spectral absorption characteristics) of negative films and reversal films are very different and while a peak is generated in a wavelength of approximately 700 nm for the spectral transmission density of C (cyan) coloring material in a negative film, for example, the spectral transmission density peak in a reversal film has a wavelength of approximately 650 nm, which is a wavelength difference of 50 nm. The reason for this is because the spectral transmission density characteristics of coloring materials of negative films are designed based on the spectral sensitivity characteristics of color paper.
Conventional devices for reading an original, however, that use an LED light source are generally structured with one LED for each of the R, G, and B wavelength regions. As an example, as is clear when the emission spectrum of each LED corresponding to each wavelength region shown in FIG. 14A is compared with the example shown in FIG. 14B of the spectral characteristics of the light emitted from a light source section formed from a halogen lamp and R, G, and B filters (these spectral characteristics are adjusted by the filters such that various types of film can be read stably), the wavelengths where the peaks are generated are very different to each other by as much as a half bandwidth (the LED emission spectrum is smaller by a half bandwidth, namely, has a narrower frequency band).
Accordingly, because the wavelengths where peaks are generated are very different and the frequency band is narrower in the spectral characteristics of the light emitted from the light source portion in a conventional device for reading an original that uses an LED as a light source as compared with the spectral absorption characteristics of the coloring material of the film being read, the accuracy with which the film is read is easily affected by differences in the type of coloring material in the film being read, variations in the LED emission spectrum caused by variations in the surrounding temperature, differences in the characteristics of each individual LED, and the like. Consequently, the problem has existed that it has been extremely difficult to always read a film accurately. Note that this problem also arises in the same way when another light emitting element other than an LED is used as a light source (i.e. a light emitting element having a narrow bandwidth emission spectrum e.g. a laser).
Moreover, when an image recorded on film is copied onto a copying material such as photographic paper, if a light emitting element such as that described above is used as the light source, the problem has arisen that there is a lack of consistency in the end product of the image that is copied onto the copying material due to the effects of differences in the type of coloring material in the film, variations in the LED emission spectrum caused by variations in the surrounding temperature, and differences in the characteristics of each individual LED.